Conventionally, a rubber hose is generally used as a radiator hose for an automobile. This is because that the rubber hose can freely be bent depending upon layout of an engine or a radiator, and the rubber hose can absorb relative displacement between the engine and the radiator caused by vibration during driving of the automobile.
However, the rubber hose is heavy in weight and handling thereof is inferior, and there is a problem that when the rubber hose is connected to a pipe of the engine or the radiator, it is necessary to clamp the hose using a hose clamp, and the mounting workability is inferior.
On the other hand, a hose made of thermoplastic resin is known. There is a known hose in which a cross section of the hose along its axial direction is formed with a waveform uneven corrugated portion so as to provided the hose with flexibility.
Such a resin hose is light in weight as compared with the rubber hose and handling thereof is superior. Further, the resin hose can previously be provided at its end with a joint portion that can be connected to the pipe of the engine or the radiator with a single motion and thus, there is a merit that the mounting workability is superior. However, since the resin hose is inferior in flexion ability to the rubber hose, it is preferable that the resin hose is previously bent into a predetermined shape in accordance with a place to be mounted.
As a bending method of a hose made of thermoplastic resin, Japanese Patent Publication No. H6-55431, e.g., discloses a method for producing a resin deformed pipe in which a helical spring having an outer diameter substantially equal to an inner diameter of a curved resin pipe is inserted and disposed into the resin pipe over its entire length, the resin pipe is mounted to a jig provided with an arc guide portion that is downwardly curved with a predetermined radius of curvature such that the resin pipe is hung between opposite ends of the guide portion, the jig to which the resin pipe is mounted is immersed in hot water, the resin pipe that is heated by the hot water and softened and bent downward by its own weight and weight of the helical spring is supported by the guide portion, and the resin pipe supported by the guide portion in the curved state it taken out from the hot water together with the jig, and in this state, the resin pipe is cooled and hardened.
Japanese Patent Publication No. H7-96261 discloses a bending method of a synthetic resin pipe in which opposite ends of the synthetic resin pipe are fixed to a clamp disposed on a base, the synthetic resin pipe is heated and softened, a screw rod is allowed to project from a bracket projected sideway from an upper surface of the base, the screw rod pushes an outer surface of the synthetic resin pipe through a resilient body connected to the screw rod, thereby bending the pipe through a desired angle. In this case, it is described that heated air is blown into the synthetic resin pipe, a current is allowed to flow through a heating sheet wound around the synthetic resin pipe to heat the synthetic resin pipe.
Further, Japanese Patent Publication No. H6-104336 discloses a method for producing a thermoplastic resin pipe having a partition that is integrally formed therein with a partition wall along its axial direction in which in a bending method of the pipe, the pipe body is heated from outside of a peripheral wall of the pipe to such a temperature that only the peripheral wall of the pipe can be deformed, the pipe having the partition is accommodated into a divided outer mold that is curved to a predetermined degree, the pipe is curved while introducing pressure fluid into the pipe body and then, the pipe is cooled and taken out.
However, in any of Japanese Patent Publication Nos. H6-55431, H7-96261 and H6-104336, there is a problem that it takes time to heat the resin hose, and if an attempt is made to heat and bend the pipe within a short time, the pipe can not be heated sufficiently and the thickness or shape of the pipe can not be precisely determined. Further, it also takes time to cool the pipe after it was bent, and there is a problem that if the cooling time is shortened and the pipe is taken out from the mold in its insufficiently cooled state, the shape of the pipe is returned to the original shape.
Therefore, it is an object of the present invention to provide a method for producing a flexion resin hose having excellent productivity capable of heating, bending and cooling the hose within a short cycle.